Cresselia is a physical tank who excels at preventing physical threats, most prominently Groudon, Rayquaza, and Garchomp, from annihilating one's team. While one would normally consider Lugia for such a role, Cresselia lacks a Rock-type weakness, meaning she takes less damage from Stealth Rock and Stone Edge, while sporting roughly the same physical durability. Due to the lack of Stealth Rock weakness, she can reliably defeat Dragon Dance Rayquaza, unlike Lugia, making her the ultimate physical wall. Cresselia also makes a great dual screener with only three weaknesses, titanic defenses, a passable Speed stat—with a Timid nature, she is capable of outrunning the many base 90 Speed Ubers that do not run a Speed-boosting nature—and perhaps most importantly, Lunar Dance, which enables a sweeper to come back into play at full health.
However, Lugia often overshadows Cresselia, due to her limited movepool, overall inferior stats, and the need for sunlight support in order to have reliable recovery in the form of Moonlight (with less PP too). As a dual screen user, she also faces significant competition, though Lunar Dance makes her unique in her role. Nevertheless, these are only limiting factors. Cresselia's movepool is more than enough to adequately support her teammates, her stats enable her to carry out her purpose, and Groudon's constant presence on the battlefield makes Moonlight more reliable in Ubers than in the sandstorm-dominated OU metagame.
While Cresselia is often compared to Lugia in terms of physical walling, she lacks the weaknesses associated with the Flying-type. She doesn't fear Stone Edge and Stealth Rock, and cannot shed her Ground-immunity with Roost. Hence, she can more reliably counter Groudon, Rayquaza, and Garchomp, the three main physical powerhouses in Ubers, and take less damage from the ever-common Ice Beam and Thunder. Even +4 Life Orb Groudon's Stone Edge will never OHKO Cresselia. Also, in the sun, Moonlight heals 66.7% of her HP, which is more efficient than Lugia's Roost.
Ice Beam is needed to counter Rayquaza, Groudon, and Garchomp. It OHKOes Rayquaza after Stealth Rock Damage and Life Orb recoil, and nets a 2HKO on Garchomp. Reflect halves the power of physical attacks, and is especially helpful against enemy Pursuit users or if rain is on the field, severely reducing Moonlight's effectiveness. Toxic is recommended for the last slot; Ice Beam does little damage to any Pokemon without a 4x Ice weakness. Furthermore, it deals more damage over time to Groudon than a single Ice Beam. Thunder Wave can hit incoming sweepers on the switch, and the two most common Pokemon in Ubers who are immune to Thunder Wave, Groudon and Garchomp, will never switch into Cresselia. Hidden Power Fire prevents Forretress from using Cresselia as set up bait and Scizor from using U-turn. Hidden Power Fire is also Cresselia's most powerful attack in the sunlight, 2HKOing 252 / 252+ Forretress. Unfortunately, in the rain, it won't even 4HKO thanks to Leftovers recovery.
The HP and Defense EVs maximize Cresselia's bulk. Cresselia can easily survive a +1 Adamant Rayquaza's Outrage after Stealth Rock damage. Cresselia will even survive a +2 Jolly Rayquaza's Outrage 87% of the time when factoring in Stealth Rock and one turn of Leftovers recovery. If she switches directly into the Outrage—meaning no Leftovers recovery—she has a 50% chance to survive%. Leftovers is the preferred item choice for the HP recovery, reducing the number of times Cresselia will have to resort to using Moonlight's precious PP. However, Shed Shell enables Cresselia to switch out of Wobbuffet.Team Options & Additional Comments >>>
Switch Cresselia in on a Pokemon who can do little to harm Cresselia, such as Blissey, Lugia, Giratina, Groudon, or even Forretress if you do not mind your opponent setting up entry hazards, then proceed to set up dual screens. Late-game, use Lunar Dance to fully heal one of your sweepers, under the protection of dual screens. The last move is up to user preference. Thunder Wave provides extra team support, paralyzing Pokemon to support a late game sweep. Additionally, by paralyzing faster opponents, Cresselia can set up a screen before they attack her. Moonlight can keep Cresselia healthy and is useful if you want to set up dual screens more than once. Ice Beam enables Cresselia to check Rayquaza, Garchomp, and Groudon without Toxic. Even with no Defense EVs, Cresselia makes a comfortable counter to Swords Dance Rayquaza, outspeeding Adamant Rayquaza and always surviving +2 Jolly Life Orb Dragon Claw after Stealth Rock damage. However, keep in mind that +1 Jolly Rayquaza's Outrage is likely to OHKO Cresselia after Stealth Rock damage, so Cresselia is not a reliable Dragon Dance Rayquaza counter. One should not use Ice Beam for the sole purpose of not Struggling when Taunted, because all the common Taunt users have nothing to fear from Cresselia's Ice Beam and can easily use a Taunted Cresselia as setup bait.
The Speed EVs enable Cresselia to outrun Adamant Rayquaza and the many base 90 Speed Ubers without a +Speed nature, so she can set up a screen before being attacked, enabling her to easily set up dual screens against Groudon, Dialga, Ho-Oh, and Rayquaza. Against these foes, you should only switch Cresselia in on them after a KO, so that you are not attacked without a screen. One can also elect to give Cresselia a Bold or Calm nature, and put all the Speed EVs into Defense and Special Defense respectively, to better protect Cresselia from one side. This is helpful for setting up against Pokemon who are always faster than Cresselia, such as Choice Scarf Dialga and Garchomp.Team Options & Additional Comments >>>
Rest can be used in place of Moonlight, but it requires cleric support. Sleep Talk provides reliable recovery alongside Rest, but Cresselia needs to immediately Ice Beam Rayquaza to reliably counter it, as Rayquaza threatens to 2HKO, and Sleep Talk will only select Ice Beam 1/3 of the time. While Rest and Sleep Talk make Cresselia effective at PP stalling, they make Cresselia even greater setup bait, and almost anything with a setup move will beat Cresselia one-on-one.
Light Screen is an option on the Ubers Wall for extra team support. Grass Knot hits most Ubers harder than Ice Beam, in particular Groudon, Kyogre, and Tyranitar. However, Cresselia will still deal very little damage with her pathetic base 75 Special Attack, and she still cannot stand up to Kyogre and Tyranitar. Cresselia's Special Attack also makes Calm Mind a poor option, as it takes many Calm Minds for Cresselia to actually dent the opposing Pokemon. Even +6 Cresselia is easily walled by Blissey, Kyogre, or Latias, while they can also set up alongside her with Calm Mind and beat Cresselia one-on-one after PP stalling Moonlight. Also, Lugia generally makes better use of Calm Mind, thanks to its higher Base Stat Total.
Cresselia also gains access to Trick Room and Gravity. When using Trick Room, use a -Speed nature and 0 IVs to ensure you are slower than neutral nature Tyranitar. Keep in mind that under Gravity, Cresselia cannot counter Swords Dance Groudon, as she can be hit by Groudon's Earthquake, and it will deal too much damage with a Swords Dance boost.
Checks and Counters
Kyogre turns the weather into rain, reducing Moonlight's recovery to a pathetic 25%, and threatens Cresselia with its STAB-boosted Water-type attacks. Tyranitar also removes the sunlight and severely dents Cresselia with STAB Crunch or Pursuit. Scizor, Heracross, and Weavile can also hit Cresselia hard with their STAB attacks while only fearing Hidden Power Fire (and Thunder Wave in Weavile's case). Blissey with Toxic also has no problems against Cresselia without Rest. However, Cresselia can easily set up dual screens and wrap up with Lunar Dance against Blissey. Forretress will easily set up on Cresselia that lack Hidden Power Fire, which will not matter if rain is up; however, Forretress itself is set up on by dual screen Cresselia. Wobbuffet shrugs off Ice Beam and can trap Cresselia with Shadow Tag, Encore any attack, and use Tickle until Cresselia loses enough Defense to be OHKOed by an opposing Pursuit user. Lunar Dance Cresselia can, however, escape from Wobbuffet by sacrificing herself. Cresselia can also carry Shed Shell to escape Wobbuffet's grasp.
Anything with Taunt will beat Cresselia, as her pathetic base 75 Special Attack means she cannot hit hard unless she hits for 4x super effective damage. Of the most common Taunt users in Ubers, which are Mewtwo, Mew, Heatran, and all Deoxys formes, all but Heatran easily use Cresselia as setup bait as long as they avoid Toxic and Thunder Wave on the switch. The same applies for Substitute users whose Substitutes can withstand an Ice Beam such as, once again, Mewtwo and Darkrai. However, Substitute does not stop Cresselia from setting up dual screens and using Lunar Dance.
It's also important to note that while Cresselia handles physical variants of Rayquaza well, Mixed Rayquaza will often 2HKO her with the combination of Draco Meteor and Outrage after Stealth Rock damage, which makes it a great Cresselia lure.